Protective and decorative coatings containing nickel



Nov. 21, 1961 w. A. WESLEY ET AL 3,009,236

PROTECTIVE AND DECORATIVE COATINGS CONTAINING NICKEL Filed Dec. 5, 1957 4 Sheets-Sheet 1 FIGURE I WACLAW ANDREW WESLEY BURTON BOWER KNAPP ROBERT JAMES McKAY INVENTORS BY (NAM ATTORNEY Nov. 21, 1961 w. A. WESLEY ET AL 3,

PROTECTIVE AND DECORATIVE COATINGS CONTAINING NICKEL Filed Dec. 5, 1957 4 Sheets$heet 2 FIGURE 2 'WACLAW ANDREW WESLEY BURTON BOWER KNAPP ROBERT JAMES McKAY INVENTORS BY CL. Q

ATTORNEY Nov. 21, 1961 w. A. WESLEY ET AL 3,009,236

PROTECTIVE AND DECORATIVE COATINGS CONTAINING NICKEL 4 Sheets-Sheet 3 Filed Dec. 5, 1957 FIGURE 3 WACCAW ANDREW WESLEY BURTON BOWER KNAPP ROBERT JAMES McKAY INVENTORS ATTORNEY PROTECTIVE AND DECORATIVE COATINGS CONTAINING NICKEL Nov. 21, 1961 W; A. WESLEY ETAL 4 Sheets$heet 4 Filed Dec.

FIGURE 4 WACLAW ANDREW WESLEY BURTON BOWER KNAPP ROBERT JAMES McKAY INVENTORS BYQ. W ATTORNEY United States Patent 7 3,009,236 PROTECTIVE AND DECORATIVE COATINGS CONTAINING NICKEL Waclaw A. Wesley, Plainfield, and Burton B. Knapp, Westfield, N.J., and Robert J. McKay, Onancock, Va., assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware Filed Dec. 3, 1957, Ser. No. 700,352 11 Claims. (Cl. 29-1835) The present invention relates to the provision of decorative and protective metallic coatings and, more particularly, to the provision on metallic surfaces of bright composite electrodeposited coatings which have substantially improved resistance to the destructive influences of industrial and marine atmospheres and which exhibit an attractive and decorative surface appearance for long periods of time during use.

As is well known to those skilled in the art, many proposals have been made in an endeavor to provide metallic coatings capable of providing appreciable resistance to corrosive attack when subjected to various atmospheres while retaining a pleasing and decorative surface appearance. The bright metallic appearance and, particularly, the retention thereof, of parts of many manufactured articles, e.g., automobiles, household equipment, metal furniture, etc., is often a paramount consideration in their usefulness and pleasure afforded the user. However, the various metals and metal combinations which have been proposed in attempts to satisfy commercial needs have proven unsatisfactory in many applications.

Electrodeposited chromium is pleasing in appearance and offers a degree of resistance to corrosive atmospheres but fails to provide sufficient protection for underlying metals, e.g., ferrous metals, chiefly on account of the inherent porosity characterizing chromium electrodeposits. Electrodeposited nickel may also have a bright and pleasing appearance but nickel deposits on basis metals are characterized by fogging in industrial atmospheres and then by pitting at myriads of points on the surface. It has been proposed heretofore to employ composite electrodeposited metal coatings, such as nickel-chromium and copper-nickel-chromium coatings wherein the chromium is the outer layer of the composite, on ferrous metals to provide an improved combination of corrosion resistance and pleasing appearance while using a commercially practicable thickness of coating in the neighborhood of about 1 mil. However, the corrosion resistance of these prior composite coatings on steel is still unsatisfactory in applications requiring relatively long exposure to weathering in industrial atmospheres, marine atmospheres and other corrosive media. For example, in the commercially used conventional nickel-chromium composite, the thickness of which is generally about 1 mil for economic reasons, chromium reducesthe fogging tendency of nickel but the chromium layer is thin and not impervious to atmospheric and other corrosive effects and, as a consequence thereof, exposure to atmospheres containing detrimental and corrosive substances, e.g., sulfur dioxide, leads to pitting and/or perforation of the composite coating. When these pits and/ or perforations penetrate through the coating to the basis metal, e.g., steel, the latter corrodes and unsightly corrosive products exude to the surface to mar its outward appearance. The protective value of conventional composite nickel-chromium coatings increases with increasing thickness of the nickel deposit, but commercially this has not proved to be a panacea for rust spotting of the plated metal, e.g., steel, exposed to weather.

It has been proposed to employ other composite electrodeposited coatings such as those containing a copper-tin 3,009,236 Patented Nov. 21, 1961 ice alloy or a copper-zinc alloy layer as a substitute for the nickel layer in the usual nickel-chromium composites. When subjected to Weathering, these substitute composites have been found to lose their decorative appearance more quickly than the conventional composites. Electrodeposited composite coatings such as nickel-copper-nickel have been widely suggested for purposes of protecting steel from corrosive effects but it has been found that this type of coating is adversely affected by atmospheric attack and that the corrosion products of copper are themselves highly corrosive to the coating. Coatings which are customarily used without a surface finish of chromium, such as zinc and cadmium coatings, although bright when freshly prepared become dull rapidly through weathering and/ or wear.

Although many attempts were made to overcome the foregoing difficulties and other difficulties, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that bright, decorative and protective composite electrodeposited coatings which, when compared with conventional coatings of the same magnitude of thickness, manifest a markedly higher order of resistance to atmospheric attack, better protect the ferrous metal base from corrosion and longer retain a pleasing surface appearance during use can be obtained when metal of a selected class is interposed between layers of nickel in the fashion of a sandwich, the outermost nickel layer advantageously being provided with a layer of chromium.

It is an object of the present invention to provide composite electrodeposited coatings which are bright and decorat-ive and exhibit an improved high degree of corrosion resistance when exposed to atmospheric attack.

Another object of the invention is to provide metallic surfaces including metals and/ or alloys with composite electrodeposited coatings characterized by a high degree of resistance to corrosion when subjected to weathering and which retain a decorative and pleasing surface appearance for relatively long periods of time during use.

The invention also contemplates providing bright, decorative and protective composite electrodeposited coatings on metallic surfaces including metals and/ or alloys which, when compared to conventional composite coatings of comparable thickness, manifest an improved order of resistance to perforation by corrosive atmospheres, better protection of the metallic surface from corrosion and longer retention of a decorative and pleasing surface appearance during use.

The invention further contemplates providing a process for accomplishing the foregoing objects.

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the drawing, in which:

FIGURE 1 is a reproduction of a photograph taken at about /2 size depicting a comparison of a series of four test panels having composite electroplated coatings within the invention prepared using layers of gray or Watts-type nickel with a control panel having a conventional electrodeposited coating containing a single layer of Watts-type nickel (the left-hand panel in the top row of three panels) after exposure to the atmosphere for eleven months in an industrial location. All the panels were given a final chromium decorative plate before exposure;

FIGURE 2 is a reproduction of a phonograph taken at about A2 size depicting a comparison of a series of test panels similar to those of FIGURE 1 within the invention with a control panel having a single nickel layer similar to that of FIGURE 1 (the left-hand panel in the top row of three panels) after exposure to the atmosphere for ten months in a marine location;

FIGURE 3 is a reproduction of a photograph taken a! about /2 size depicting a comparison of a series of four test panels having composite electroplated coatings within the invention prepared using layers of bright nickel with a control panel having a conventional single-layer coating containing a single layer of bright nickel (the left-hand panel in the top row of three panels) after exposure to the atmosphere for eleven months in an industrial location. All the panels were given a final chromium decorative plate before exposure; and

FIGURE 4 is a reproduction of a photograph taken at about /2 size depicting a comparison of a series of four test panels similar to those of FIGURE 3 having a composite coating within the invention with a control panel having a single layer of bright nickel similar to that of FIGURE 3 (the left-hand panel in the top row of three panels) after exposure to the atmosphere for ten months in a marine location.

Generally speaking, the composite electrodeposited coatings provided in accordance with the present invention are comprised of a plurality of nickel layers and a layer of electrodeposited chromium interposed between said layers of nickel. A relatively thin layer of chroinium having a thickness of about to 20* micro-inches is advantageously deposited on the outermost layer of nickel. When the composite coatings of the present invention are electrodeposited on a metallic base, including metals and/ or alloys, it has been found that the coatings are more resistant to atmospheric and other corrosive effects and retain a pleasing protective surface appearance longer during use than do known bright coatings of the same order of thickness, e.g., the conventional nickel-chromium and copper-nickel-chromium electrodeposits containing a single nickel layer. It is important within the concepts of the presentinvention in order to insure the attainment of highly satisfactory results that the respective thicknesses of each of the electrodeposited metal layers comprising the composite coating be controlled within the following ranges:

Mils Basis layer of electrodeposited nickel 0.1 to 2 Intermediate chromium layer 0.001 to 0.1 Outer layer of electrodeposited nickel 0.1 to 2 The composite coating must in all cases be at least 0.25 mil thick.

In carrying the invention into practice, it is advantageous in order to achieve optimum results to control the thickness of the intermediate chromium layer within the range of 0.001 to about 0.03 mil. When intermediate or interposed chromium layers of the aforementioned thickness are employed, superior results are obtained using a basis nickel layer having a thickness of about 0.1 to 1 mil' and an outer nickel layer having a thickness of about 0.1 to 2 mils. In general, for best protective effects, thicker outer nickel layers should be employed when the basis nickel layer has a thickness in the lower portion of the range described. For example, when the basis nickel layer is only about 0.2 mil or 0.1 mil or even as thin as about 0.05 mil, the outer nickel layer should be at least about 0.5 mil, or more advantageously about 0.6 or 0.75 or 1 mil thick. The total thickness of nickel in the two layers should be at least about 0.5 mil but most advantageously is about 1 mil, particularly when the coating is to be subjected to outdoor exposure. When composite coatings having layer thicknesses within the foregoing preferred ranges are employed, we have found that the results obtained are not only markedly superior to the results obtained utilizing conventional composites, e. g., nickel-chromium composites, of comparable thickness, e.g., about 1 mil, but are comparable and often superior to conventional composites, e.g., nickel-chromium, of twice the thickness, e.g., about 2 mils. The effectiveness of the chromium intermediate layer is greatest when the thickness thereof is maintained in the range of 0.005 to 0.015 mil.

The nickel layers contemplated by the invention may be made of electrodeposited nickel obtained from sulfatechloride plating baths of the conventional Watts-type, or may be made of nickel deposited from the all-chloride bath or the all-sulfate bath, or may be made of bright nickel deposited from baths containing the usual brighteners or levelers for enhancing the appearance of the nickel electrodeposit. Nickel plating baths for producing nickel deposits satisfactory for use in the present invention contain up to 400 grams per liter of nickel sulfate (NiSO .7H O), up to 400 grams per liter of nickel chloride (NiCl .6H O) and up to 50 grams per liter (preferably 10 to 40 grams per liter) of a buffer such as boric acid. Those skilled in the art know that the essential ingredients of the Watts-type nickel plating bath are nickel sulfate (NiSO .7H O) and nickel chloride (NiCl .6H O) which may be present in the bath in amounts of about to about 400 grams per liter and of about 10 to about 60 grams per liter, respectively. The bath is operated in the pH range of about 1.5 to 6. Usually a buffering agent such as boric acid is included in the bath in an amount of up to about 50 grams per liter, e.g., about 10 to about 40 grams of boric acid per liter. A small amount (e.g., about 0.2 gram per liter) of a wetting agent such as a sodium lauryl sulfate is usually included in the bath to prevent undesirable pitting.

Cathode current densities of about 20 to about 100 amperes per square foot are usually employed and the operating range of bath temperatures is about to about 160 F. Nickel deposited from the Watts-type bath generally will require buffing before application of the final chromium plate to insure a fully bright appearance. Plating baths for plating bright nickel are of generally similar composition to the Watts-type bath, and may, for example, contain about 25 to 300 grams per liter of nickel sulfate (NiSO .7H O) and 30 to 225 grams per liter of nickel chloride (NiCl 6H O), with up to 50 grams per liter of boric acid as a buffer. Bright nickel baths include combinations of addition agents for producing a more lustrous and brighter deposit than is obtainable with the Watts-type bath. These addition agents generally include a combination of a wetting agent, a leveling and/ or smoothing agent, a luster-producing agent and a stress-reducing agent. Bright nickel plating baths are discussed in Modern Electroplating, John Wiley and Sons, Inc., New York, 1953, at pages 311 to 318 and in many US. patents, including, e.g., Patents No. 2,191,813, No. 2,389,135, No. 2,524,619, No. 2,647,866 and No. 2,648,628.

Plating baths for producing semi-bright nickel are generally similar in composition to Watts-type baths and bright nickel baths and contain a leveling agent, such as coumarin and derivatives thereof, which contributes a leveling and scratch-covering property to the plate without introducing a high level of stress therein as may be the case with bright nickel. Semi-bright nickel plates are not as bright as the bright nickel plates, but are more easily buffed than conventional Watts-type plates, and are characterized by a high degree of smoothness. Nickel electrodeposits from the Watts-type bath generally have a hardness of about to Vickers, while bright nickel electrodeposits generally have a higher hardness which may be as high as about 500 Vickers.

Modern production conditions favor the use of bright or semi-bright nickel deposits since these deposits require no bufiing or very little bulfing as compared to the conventional gray or Watts-type nickel deposits. A particular embodiment of the invention wherein a satisfactory composite coating upon an underlying metal, e.g., steel, is provided without any mechanical polishing operation, e.g., bufiing, includes the following steps:

( 1) Prepare the underlying metal for plating,

(2) Deposit a layer of gray or Watts-type nickel thereon in a thickness as hereinbefore described,

(3) Deposit an intermediate layer of chromium of the hereinbefore described thickness,

(4) Deposit a bright outer nickel layer of the hereinbefore described thickness, and

(5) Deposit an outer chromium layer over the said bright nickel layer.

The aforedescribed outer nickel layer may advantageously comprise a layer of semi-bright nickel applied over the intermediate layer in suflicient thickness to provide a good leveling action, e.g., about 0.5 mil, and a layer thereover of bright nickel to provide a bright finish upon which the final chromium layer may be applied. Alternatively, layers of bright nickel may be employed in accordance with the invention.

The invention also contemplates multi-layer coatings havings a plurality of electrodeposited intermediate layers of the kind and thickness described hereinbefore and having a plurality of electrodeposited nickel layers having thicknesses as aforedescribed. As an example, a multilayer composite on steel comprising a layer on the steel of electrodeposited nickel 0.1 mil thick, a layer thereon of electrodeposited chromium 0.01 mil thick, another layer of nickel 0.1 mil thick, a further layer of chromium 0.01 mil thick, and an outer layer of nickel 1 mil thick, with a decorative coating of chromium micro-inches thick is a satisfactory multi-layer composite in accordance with the invention.

In preparing the composite electrodeposited coatings in accordance with the invention, it is of the utmost importance that sound adhesion of each layer to each other layer be obtained. This is of particular importance in applying an outer nickel layer upon an intermediate layer of chromium. For the purpose of securing satisfactory adhesion of a nickel outer layer upon an intermediate chromium layer, the chromium layer was subjected to the following treatment in producing satisfactory composite coatings in accordance with the invention:

(1) Water rinse after chromium plating.

(2) Dip for one minute in an acid aqueous nickel plating bath containing about 240 g.p.l. NiCl 6H O and about 36 g.p.l. HCl at about 7080 F., cathodically treat the chromium plate in the bath for 6 minutes at 30 a.s.-f. using nickel anodes.

(3) Water rinse.

(4) Transfer to the nickel plating bath.

In order to demonstrate the improved results achieved in carrying out the concepts of the present invention, an extensive testing program was conducted to establish the resistance of composite electrodeposited coatings within .the invention and to compare the resistance to atmospheric corrosion of these composites with other composites outside the scope of the present invention and with control tests of conventional nickel-chromium electrodeposited coatings. In all cases a stain resistant chromium coating about 10 to 20 micro-inches thick was applied as the outer layer. Except where otherwise specified, the nickel layers employed were of the conventional Watts-type or gray nickel. Data obtained as a result of this testing program is tabulated hereinafter in Tables I to VII. Testing was carried out both in an industrial atrnopshere at Bayonne, New Jersey, and in a marine atmosphere at Kure Beach, North Carolina. The test specimens for the most part were electrodeposited upon panels of polished SAE 1010 steel in the form of /8" x 4" x 6" plates. One of the sets of test specimens comprised foils which were made by electrodepositin'g coatings to be tested on a highly polished cobalt-chromium alloy starting sheet from which electrodeposited foils could easily be stripped. Conventional cleaning and plating methods well known to those skilled in the art were employed in the preparation of the test panels and foils. Thus, the steel panels were prepared for plating according to the following procedure:

(1) Polish the panels with grit belts, finishing with a .320-grit belt.

(2) Vapor degrease.

(3) Pumice scrub and hot water rinse.

(4) Cathodically clean in a solution of sodium car- .bonate containing 60 grams per liter Na CO for 25 minutes at 160 F. and 25 'amperes per square foot.

(5 Anodically clean the panels in the sodium carbonate solution for 5 minutes at 20 amperes per square foot.

(6) Dip in a solution containing 50% hydrochloric acid by volume for 30 seconds at -115 F.

After exposure of the p lated steel panels in the atmosphere and :for the times indicated in the following tables, the panels were examined to compare the corrosion resistance of the coatings deposited thereon with each other and with the nickel-chromium control panels of the conventional type. The examination comprised a visual inspection wherein the panels were given a merit rating designating the relative order and the appearance of each panel, with the panel exhibiting the best appearance being designated by the numeral 1. In addition, the panels were rated according to the method recommended by the American Society for Testing Materials Committee B8, Subcommittee II, described in the Proceedings of the A.S.T.M., vol. 49, 1949, at pages 220 et seq. The [following comparison of percentage corrosion-afiected area and rating numbers was employed in evaluating the panels described in Tables I to VII hereinafter:

The results obtained in the testing program, as set forth in Tables I to VII, are as follows:

TABLE I Tests of electrodeposits on steel exposed for 18 months in an industrial atmosphere. This set included composite electrodeposited nickel coatings of the sandwich type containing intermediate layers of chromium, copper, zinc, iron, a nickel-iron alloy containing about 16% iron, and a conventional nickel-chromium composite control panel (panel No. 3 in Table I). All the coatings were deposited to a thickness of 1 mil to afiord a comparison. It was found that the composite containing an intermediate layer of chromium was markedly superior in all respects as compared to the conventional nickel-chromium deposit. On the other hand, the composites containing intermediate layers of zinc, iron-nickel alloy, copper and iron were inferior to the conventional nickel-chromium deposit.

TABLE II Tests on electrodeposited foils exposed :for 12 months in an industrial atmosphere. This set contained composite foils prepared to the same specifications as the composite coatings set forth in Table I. The foils were inspected by placing them against a strong light in a darkroom. A No. 2 photofiood bulb was used in a photographic printing box and the foil was masked to facilitate detecting and counting of the perforations. Examination of the oils established that the composite foil containing a chromium intermediate layer was substantially more resistant to perforation as a result of the atmospheric exposure than was the conventional nickel-chromium foil (panel 9 of the same thickness. In addition, it was observed that the foils containing intermediate layers of zinc, iron-nickel alloy, copper and iron were badly perforated.

TABLE III Steel panels having composite electrodeposited coatings exposed for 12. months to a marine atmosphere. This set included 1 mil thick composite electrodeposited coatings of the sandwich type including intermediate layers of chromium and copper. A panel (panel No. having the conventional nickel-chromium electrodeposited coating of the same 1 mil thickness was also included. Examination of these panels showed that panel No. 13 having the composite coating containing [the chromium intermediate layer was greatly superior in its protective and decorative effect to the conventional nickel-chromium electrodeposit and to the composite coating containing the copper intermediate layer.

TABLES IV AND V Tests of coated steel panels for 12 months in an industrial atmosphere and in a marine atmosphere, respectively. This set included sandwich-type composite electrodeposit'ed coatings containing intermediate layers of chromium. All of the layers were deposited to a thickness of 1 mil and the thickness of the intermediate layer was varied between 0.01 and 0.1 mil. Control specimens of conventional nickel-chromium deposits having a thickness of 1 mil and 2 mils were included (panels A, 20B, 21A and 21B, and panels 26 and 27, respectively, in Tables IV and V). Duplicate sets of test samples were employed in the industrial atmosphere. Inspection of these panels demonstrated that the composite coatings containing chromium as the intermediate layer displayed the best visual rating in both the marine and the industrial atmosphere and, in addition, displayed the best rating under the A.S.T.M. suggested system. It was noted that the intermediate chromium layer having a thickness of about 0.01 mil (panels 16A, 16B and 22, respectively, in Tables IV and V) demonstrated superior performance. The composite coating containing 0.01 mil chromium as the intermediate layer was substantially superior in both the industrial and marine atmosphere to the control sample having the same thickness and even to the control sample having twice the nickel thickness.

TABLES VI AND VII Tests in both the industrial (11 months) and the marine (10 months) atmosphere comparing, respectively, the corrosion resistance of sandwich-type composites made, respectively, with the standard Watts nickel and with bright nickel. In these series of tests, chromium in the thickness range from 0.001 mil to 0.1 mil was used as the intermediate layer in the sandwich-type deposits. In addition, panels having intermediate chromium layers obtained by using commercial proprietary crack-free chromium baths (which contain a self-replenishing catalyst) in the thickness of 0.025 mil were included in each test. Control panels having a thickness of l, 2 and 3 mils of Watts nickel (panels 37 I and M, 38 I and M and 39 I and M) and of bright nickel (panels 49 I and M, 50 I and M and 51 I and M), respectively, and with the usual chromium outer coating, were employed in each series of tests. In Table VI, tests wherein a chromium intermediate layer 0.01 mil thick was positioned closer to the basis metal (panels 36 I and M) were also included.

The results of the tests indicated that the bright nickel is generally as resistant to corrosion as the Watts-type nickel. It was again observed that the sandwich-type protective and decorative deposits contemplated in accordance with the present invention displayed greatly improved corrosion resistance as compared to a conventional-type deposit having the same thickness. Coatings having chromium intermediate layers produced using the proprietary crack-free baths behaved quite similarly to coatings containing a chromium intermediate layer produced with the standard chromium bath. The panels made with the chromium layer placed closer to the basis metal (panels 36 I and 36 M) appeared to offer an advantage, particularly in the marine atmosphere.

FIGURE 1 of the drawing comprises reproductions of photographs of certain of the panels made using the Watts-type nickel which were included in Table VI after the panels were exposed in an industrial atmosphere. Coatings 1 mil thick were originally plated on these panels. The upper left-hand panel is panel 37 I and the remaining panels (proceeding from panel 37 I in order from left to right) are panels 32 I, 28 I, 29 I and 30 I. The control panel (panel 37 I) exhibited much heavy rust stain accompanied by much crater rusting. Panel 32 I represents an improvement over the control panel and the crater-type of rusting was not as severe. This panel could be more readily restored to a decorative appearance than could the control panel. The further improvement represented by panels 28 I, 29 I and 30 I having composite coatings within the invention as compared to the control panel, which had a single nickel layer, is readily apparent from the drawmg.

FIGURE 2 of the drawing comprises reproductions of photographs of similar panels made using Watts nickel and included in Table VI after the panels were exposed in a marine atmosphere. The upper left-hand panel is the control panel (panel 37 M), which had a single nickel layer, and the remaining panels (proceeding from panel 37 M from left to right) are panels 32 M, 28 M, 29 M and 30 M. The control panel (panel 37 .M) was badly cratered and its decorative value was destroyed. The panels having composite coatings within the present invention, on the other hand, retained a high proportion of their original decorative and protective value. Panel 28 M, which had an intermediate layer of chromium 0.01 mil thick, was affected only very slightly by the exposure.

FIGURE 3 of the drawing comprises reproductions of photographs of certain of the panels made using bright nickel which were included in Table VII after the panels were exposed in an industrial atmosphere. Coatings 1 mil thick were originally plated on these panels. The up per left-hand panel is the control panel having a singlelayer nickel coating (panel 49 I). The remaining panels had composite coatings within the invention and, proceeding from panel 49 I from left to right, these panels are, respectively, panels 42 I, 43 I, 44 I and 45 I. The improvement in the protective and decorative value represented by the composite coatings provided in accordance with the invention as compared to the control panel is readily evident from the drawing.

FIGURE 4 of the drawing comprises reproductions of photographs of panels similar to those of FIGURE 3 and made using bright nickel. These panels are also included in Table VII. The control panel having a single nickel layer (panel 49 M) is again at the upper lefthand corner. The panels having composite coatings within the invention are, proceeding from left to right from the control panel, panels 42 M, 43 M, 44 M and 45 M. The decorative value of the control panel was destroyed by the exposure and deep crater rusting is evident as a result of the exposure. The composite coatings within the invention, on the other hand, retained their decorative value to a greatly improved extent, as is evident from the drawing.

Comparison of FIGURES 1 and 3 with the corres' ponding FIGURES 2 and 4 strikingly demonstrates the variation in the manner of corrosive attack displayed in the industrial atmosphere as compared to that displayed in the marine atmosphere. This comparison also indicates the complicated nature of the problems involved in providing improved decorative and protective coatings containing nickel layers.

The panels were examined in the as-exposed condition since this condition represents the appearance of the panels as they would be in use. Many of the panels were also cleaned and examined again. Cleaning improved the appearance of the panels but it was noted that, on re-exposure for a relatively short time, the conventional nickel-chromium control panels exhibited a much greater amount of rust staining than was the case with the composite coatings containing an intermediate layer embedded in the nickel. The diite-rence was particularly marked when the control panels were compared to the composite coated panels having an intermediate chromium layer.

TABLE I Results of exposure of composite electrodeposits on steel to Bayonne atmosphere Panels-Not cleaned Exposure-18 months Final nickel layer buffed and chromium plated with 15 micro-inches of chromium Corrosion of composite electrodeposited foils in Bayonne atmosphere Exposure12 months Foil taped on glass plates for exposure Foil size-2" x 4.5"

Final nickel layer buffed and chromium plated with 0.000020 inch chromium Periorations Panel Order of depositing layers Thickness,

N o. mils Ni-Fe-Ni 4-. 1-. 5 540 1.440

1 Heat treated after plating (2 hours at 300 F.).

TABLE III Results of exposure of composite electrodeposits on steel to Kure Beach atmosphere PanelsNot cleaned Exposurel2 months Panel size-4" x 6 SteelSAE 1010 Final nickel layer boiled and plated with 20 micro-inches of chromium Panel Order of depositing layers Thickness, Visual ASTM No. mils rating 1 rating Ni-Cr-Ni 4-. 1. 5 1 8. 6 N i-Ou-Ni 4-. 1-. 5 2 2. 1 Nickel. 1 3 2 10 TABLE iv Visual ASTM Panel Order of depositing Thickness, rating rating No. layers mils V I Set A Set B Set A Set B 16... Ni-Or-Ni 49-. 01-. s 1 1 10 10 17. Ni-Cr-Ni. 475-. 025-. 5 4 3 5. 6 5. 6 18; Ni-Cr-Ni. 45-. 05-. 5 5 5 3. 6 2. 7 19- Ni-Cr-Ni. 4-. l-. 5 2 2 8. 4 8. 5 20."- NickeL 1.0 6 6 2.7 2.2 21 do 2.0 3 4 2.8 4.8

TABLE v Results of exposure of composite nickel coatings on steel to Kure Beach atmosphere Panels-Not cleaned, Exp0sure12 months Final nickel layer buffed and plated with 10-12 micro-inches of chromium Panel Order of depositing layers Thickness, Visual A 8 TM N o mils rating rating TABLE VI Composite coated steel panels made using Watts-type nickel Final nickel layer buffed and plated with 10 micro-inches chromium Industrial Marine atmosphere atmosphere Panel Order of depositing Thickness, mils (11 months) (10 months) No. layers "1 series, M" series,

ASTM ASTM rating rating Ni-Or-Ni. 0. 49-0. 01-0. 5 6 v 9 Ni-Cr-N 0. 5-0. 005-0. 5 7 8 Ni-Cr-N 0.5-0. 0025-0. 5 7 7 1 Plated from crack-free proprietary bath.

TABLE VII Composite coated steel panels made using bright nickel Final layer 10 micro-inches of chromium 1 Visual rating in order of merit with No. 1 best.

1 Plated from crack-fresh proprietary hath.

11 The electroplating baths and conditions of plating employed in producing the test panels described in Tables I to VII are as follows:

WATTS-TYPE NICKEL BATH Plating composition:

BRIGHT NICKEL (TABLE VII) Plating bath:

NiSO -7H O g.p.l. 90 NiCl -6H O g.p.l. 206 H3BO3 g'pl.

Brightening agent (a mixture of saccharin, benzene sulfonamide and paratoluene sulfonamide) g.p.l. 6 Luster-producing agent containing pyridinium and quinolinium compounds mL/l. 1.25

Wetting agent (a mixture of agents exemplified by a sodium salt of lauryl sulfoacetate and a sodium salt of monolauryl ether of ethylene glycol monosulfate) ml./l. Plating conditions:

Temperature ..F. 140 pH 3.5 Current density a.s.f. 50 Residual corrected stress in deposit p.s.i. 7,500 to 9,500

STANDARD CHROMIUM Plating bath:

CTO3 g.p.l.

S0 g.p.l. 2.5 Plating conditions:

Temperature F. 113

Current density a.s.-f. 144

1 Compressive.

The present invention is particularly applicable for the purpose of providing composite electrodeposited coatings on structural metals which are susceptible to atmospheric attack when exposed by themselves. Such foundation metals include copper, zinc, aluminum, brass, etc., and alloys such as steel, e.g., carbon steels and low alloy steels containing phases associated with alpha iron, etc. The composite electrodeposits of the invention are suitable for use in both industrial and marine atmospheres.

Although the phenomena underlying the improved re sults which are obtained in carrying out the present invention arevery complicated and are not fully understood, it is believed that the improvements flowing from the present invention are related to the use as the intermediate layer of the special composite coating a metal having a definite galvanic relationship to nickel. Thus, metals such as zinc, iron and iron-nickel alloys are too strongly anodic to nickel and are unsatisfactory for purposes of the present invention. Copper also is unsatisfactory for purposes of the present invention, although the electrochemical explanation therefor is obscure. Thus, copper appears to act cathodically to nickel at some times and anodic at other times. Chromium is the metal most satisfactory for the intermediate layer to be sandwiched between nickel layers in accordance with the invention and appears to display a potential which is close to that of nickel but is cathodic to nickel.

The beneficial effects brought about by the invention are not 'explainable on the simple basis of interrupting the continuity of the nickel coating, although this factor is involved. The available data indicate that the kind of metal used in the intermediate layer and the thickness of the intermediate layer are of primary importance in carrying out the invention to produce protective and decorative electrodeposited coatings having a total thick ness of about 1 mil, e.g., at least about 0.25 mil to 3 or 4 mils.

The preferred composite or sandwichtype electrodeposited coatings described hereinbefore are useful in, and satisfactory for, the usual commercial applications such as automotive bumpers and trim where a decorative and/or protective coating resistant to atmospheric corrosive effects is required. Other applications include trim and outer shells for electrical appliances and the like, and including refrigerators, toasters, stoves, etc.; metal furniture; plumbing fixtures; household hardware; industrial hardware; etc., where a bright, attractive metal finish which is durable in service is required. The outer chromium coating described hereinbefore is generally required where stain resistance to atmospheric corrosive efiects is a criterion.

The nickel and chromium coatings contemplated in accordance with the invention advantageously are produced by electrodeposition. However, it is to be understood that chemically deposited nickel coatings such as those described in the Brenner et al. U.S. Patent No. 2,532,283, coatings produced by high vacuum vaporizing, and coatings produced by thermal decomposition of metal carbonyls, e.g., nickel carbonyl, may also be employed to produce metal layers in accordance with the invention.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. As a new article of manufacture, a metal article having firmly bonded to the surface thereof a protective and decorative composite metal coating, said coating comprising a foundation layer of nickel about 0.1 to about 2 mils thick deposited on said surface, an electron deposited layer of chromium about 0.005 to about 0.015 mil thick applied to said nickel layer, and an outer layer of nickel about 0.1 to 2 mils thick applied to said chromium layer, said composite coating being characterized by an improved decorative and protective effect as compared to a coating having a single nickel layer of the same thickness.

2. As a new article of manufacture, a metal article having firmly bonded to the surface thereof a protective and decorative composite metal coating, said coating comprising a foundation layer of nickel about 0.1 to about 2. mils thick deposited on said surface, an electrodeposited layer of chromium about 0.001 mil to about 0.03 mil thick applied to said nickel layer, and a layer of nickel about 0.1 to about 2 mils thick applied to said chromium layer, said composite coating having an improved decorative and protective effect as compared to a coating having a single nickel layer of the same thickness.

3. As a new article of manufacture, an article of metal from the class consisting of copper, brass, zinc, aluminum and steel having firmly bonded to the surface thereof a protective and decorative composite metal coating, said coating comprising a foundation layer of nickel about 0.1 to 2 mils thick deposited on said surface, an electrodeposited layer of chromium about 0.005 to about 0.015 mil thick applied to said nickel layer, and an outer layer of nickel about 0.1 to 2 mils thick applied to said chromium layer, said composite coating being characterized by an improved decorative and protective effect as com pared to a coating having a single nickel layer of the same thickness.

4. As a new article of manufacture, an article of metal from the class consisting of copper, brass, zinc, aluminum and steel having-firmly bonded to the surface thereof a composite metal coating at least about 0.25 mil up to about 4 mils thick, said coating comprising a plurality of nickel layers and at least one intermediate chromium layer about 0.005 mil to about 0.015 mil thick, and said composite coating having an improved decorative and protective effect as compared to a coating having a single nickel layer of the same thickness.

5. As a new article of manufacture, a metal article having firmly bonded to the surface thereof a composite metal coating at least about 0.25 to about 4 mils thick, said composite metal coating comprising a plurality of nickel layers and at least one intermediate chromium layer about 0.001 mil to about 0.03 mil thick, and said composite coating being characterized by an improved decorative and protective effect as compared to a coating having a single nickel layer of the same thickness.

6. As a new article of manufacture, a metal article having firmly bonded to the surface thereof a composite metal coating at least about 0.25 to about 4 mils thick, said composite metal coating comprising a plurality of nickel layers and at least one intermediate chromium layer about 0.001 mil to about 0.1 mil thick, and said composite coating being characterized by an improved decorative and protective eifect as compared to a coating having a single nickel layer of the same thickness.

7. In the method for applying a protective metal coating upon a metal article, the improvement for providing a metal coating having an enhanced protective and decor-ative effect which comprises depositing an adherent nickel layer upon said metal article, depositing upon said nickel layer a chromium layer about 0.001 mil to about 0.03 mil thick, and depositing an adherent nickel layer upon said chromium layer to produce a composite protective metal coating about 0.25 mil to about 4 mils thick, said composite metal coating being characterized by an enhanced protective efiect as compared to a coating having a single nickel layer of the same thickness.

8. In the method for applying a protective metal coating upon a metal article, the improvement for providing a metal coating having an enhanced protective and decorative effect which comprises depositing an adherent nickel layer upon said metal article, depositing upon said nickel layer a chromium layer about 0.001 mil to about 0.1 mil thick, and depositing an adherent nickel layer upon said chromium layer to produce a composite protective metal coating about 0.25 mil to about 4 mils thick, said composite metal coating being characterized by an enhanced protective effect as compared to a coating having a single nickel layer of the same thickness.

9. In the method for applying a protective metal coating upon a metal article, the improvement for providing a metal coating having an enhanced protective and decorative effect which comprises depositing an adherent nickel layer upon at least a portion of said metal article, depositing upon said nickel layer an adherent chromium layer about 0.005 mil to about 0.015 mil thick, and depositing an adherent nickel layer upon said chromium layer to produce a protective metal coating at least about 0.25 mil to about 4 mils thick, said composite metal coating being characterized by an enhanced protective eifect as compared to a coating having a single nickel layer of the same thickness.

10. In the method for applying a decorative and protective metal coating upon a metal article of the class consisting of copper, brass, zinc, aluminum and steel, the improvement for providing a metal coating having an enhanced decorative and protective effect which comprises depositing an adherent nickel layer about 0.1 to about 2 mils thick upon at least a portion of said metal article, electrodepositing an adherent chromium layer about 0.001 mil to about 0.03 mil thick upon said nickel layer, depositing an adherent nickel layer about 0.1 to about 2 mils thick upon said chromium layer, and electrodepositing an outer chromium layer upon said article to provide a composite metal coating having an enhanced decorative and protective effect as compared to a coating having a single nickel layer of the same thickness.

11. In the method for applying a decorative and protective metal coating upon a metal article of the class consisting of copper, brass, zinc, aluminum and steel, the improvement for providing a metal coating having an enhanced decorative and protective effect which comprises depositing an adherent nickel layer about 0.1 to about 2 mils thick upon at least a portion of said metal article, electrodepositing an adherent chromium layer about 0.005 mil to about 0.015 mil thick upon said nickel layer, depositing an adherent nickel layer about 0.1 to about 2 mils thick upon said chromium layer, and electrodepositing an outer chromium layer upon said article to provide a composite metal coating having an enhanced decorative and protective elfect as compared to a coating having a single nickel layer of the same thickness.

References Cited in the file of this patent UNITED STATES PATENTS 1,802,695 Bennett Apr. 28, 1931 1,991,747 Hogaboom Feb. 19, 1935 2,188,399 Bieber Jan. 30, 1940 2,336,568 Pray Dec. 14, 1943 2,428,033 Nachtman Sept. 30, 1947 2,859,158 Schaer Nov. 4, 1958 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N0o 3 OO9 236 November 21 1961 Waclaw A. Wesley et, a1

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 66,, for "phonograph" read photograph 3 column 6 lines 11 and 12 for "atmosphere" read atmospheres column 12 lines 44 and 45 for "electron deposited read electrodeposited Signed and sealed this 1st day of May 1962,

(SEAL) Attest:

ERNEST wo SWIDER DAVID D Attesting Officer Commissioner of Patents 

1. AS A NEW ARTICLE OF MANUFACTURE, A METAL ARTICLE HAVING FIRMLY BONDED TO THE SURFACE THEREOF A PROTECTIVE AND DECORATIVE COMPOSITE METAL COATING, SAID COATING COMPRISING A FOUNDATION LAYER OF NICKEL ABOUT 0.1 TO ABOUT 2 MILS THICK DEPOSITED ON SAID SURFACE, AN ELECTRON DEPOSITED LAYER OF CHROMIUM ABOUT 0.005 TO ABOUT 0.015 MIL THICK APPLIED TO SAID NICKEL LAYER, AND AN OUTER LAYER OF NICKEL ABOUT 0.1 TO 2 MILS THICK APPLIED TO SAID CHROMIUM LAYER, SAID COMPOSITE COATING BEING CHARACTERIZED BY AN IMPROVED DECORATIVE AND PROTECTIVE EFFECT AS COMPARED TO A COATING HAVING A SINGLE NICKEL LAYER OF THE SAME THICKNESS. 